D.-c. cold-cathode tube voltage regulator



March 11, 1958 M. MILLER 2,826,734

D.-C. COLD-CATHODE TUBE VOLTAGE REGULATOR,

Filed July 1, 1952 2 Sheets-Sheet 1 'INVENTOR MYRON MILLER ATTORNEYSMarch 11, 1958 M. MILLER 2,826,734

D.C. COLD-CATHODE TUBE VOLTAGE REGULATOR Filed July 1, 1952 2Sheets-Sheet 2 FIG.3.

LOAD

A no |B\ I00 D LLI 3 J O D O. D O

[so 140 I30 120 I0 BATTERY VOLTAGE INVENTOR MYRON MILLER ATTORNEYSUnited States Patent Ofilice D.-C. COLD-CATHODE TUBE VOLTAGE REGULATORMyron Miller, Silver Spring, Md., assignor to the United States ofAmerica as represented by the Secretary of the Navy Application July 1,1952, Serial No. 296,779

Claims. (Cl. 323-17) (Granted under Title 35, U. S. Code (1952), see.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention comprises novel and useful improvements in voltageregulators and more particularly pertains to a cold-cathode type D.C.voltage regulator.

Cold-cathode tubes have a substantially constant voltage drop over awide range of current and consequently can be utilized as voltageregulators. One such arrangement utilizes a cold-cathode tube in serieswith a regulating resistor across a D.-C. voltage source to be regulated. Such an arrangement produces a substantially constant voltageoutput which appears across the coldcathode tube and which outputpotential is determined by the conduction potential of the tube. Aplurality of cold-cathode tubes may be connected in series to produce aregulated output voltage which is a multiple of the individual tubeconduction potential.

The breakdown potential of cold-cathode tubes is greater than theconduction potential thereof and consequently special provision must bemade for igniting the tubes when a plurality of tubes are connected inseries and the supply voltage being regulated does not exceed thecombined breakdown potentials of the tubes, Additionally, in someapplications in which the load is continuously connected to theregulator so that load current begins to flow through the regulatorcircuit when the regulator is connected to the D.-C. voltage source, thedrop across the regulating resistor due to the flow of load currenttherethrough further reduces the voltage applied to the cold-cathodetubes and further increases the prob lem of igniting the tubes.

An important object of this invention is to provide a cold-cathode tubeD.-C. voltage regulator in which the tubes are automatically ignitedupon connection of the voltage regulator to the D.-C. voltage sourcebeing regulated.

Another object of this invention is to provide a coldcathode tube D.-C.voltage regulator which requires low power for operation.

A further object of this invention is to provide an automaticallyigniting cold-cathode tube voltage regulator which will ignite underload on low supply source voltage.

Still another object of this invention is to provide a cold-cathode tubeD.-C. voltage regulator which will not be extinguished due to suddenload surges.

Other objects and many of the attendant advantages of this invent onwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

Fig. 1 is a schematic view of one form of cold-cathode tube voltageregulator;

Fig. 2 is a schematic view illustrating a modified form of voltageregulator;

Fig. 3 is a schematic view illustrating a further modified form ofvoltage regulator; and

2,825,734 Patented Mar. 11, 1958 Fig. 4 is a curve illustrating thevariation in output voltage with decreasing supply potential.

Reference is now made more specifically to Fig. 1 of the drawings. Apair of cold-cathode tubes 10 and 11 respectively having plates l2, l3,grids 14, 15 and cathodes 16, 17 are diode connected in a series circuitwith each other and with regulating resistor 18. Certain types ofcold-cathode tubes have a substantially constant conduction potential asthe control gap current is varied over a Wide range and have asubstantially uniform breakdown potential which exceeds the conductionpotential. In order to effectuate ignition of series connected cold-cathode tubes from a D.-C. supply source B having a nominal output voltagewhich is less than the combined breakdown potentials of the seriesconnected tubes, a resistance 19 is provided in shunt with tube 10. Whenthe D.-C. voltage source B is connected to the regulator circuit as byswitch S potential is applied to tube 11 by way of resistors 18 and 19causing tube 11 to ignite, thereby reducing the potential dropthereacross to the conduction potential of the tube.

A load 21 is connected across the voltage regulator tubes by way or" anR.-C. filter circuit comprising ballast resistor 22 and condenser 2.3,which filter circuit serves to prevent load surges from extinguishingthe voltage regulator. Since the starting load current [including thecharging current of condenser 23] begins to flow when the voltageregulator is connected to supply source B there is a voltage drop acrossresistor 18. In order to cause both voltage regulator tubes to fire evenwhen the supply voltage exceeds the sustaining voltage of tube 11 andthe breakdown voltage or" tube 10 by only a few volts, a series R.-C.circuit comprising resistor 24 and condenser 25 is provided in shuntwith resistor 18. The capacitance of condenser 25 is made large so thatthe voltage drop thereacross is small during the interval in whichconduction is successively established in tubes 11 and 10. The seriesresistor 24- is provided to prevent the rapid discharge of condenser 1.5which would tend to extinguish the regulator tubes 10 and 11, and ismade small as compared to the resistance 18. Thus, during a transientperiod after connecting the voltage regulator to the supply source B theseries circuit including resistor 24 and condenser 25 effectively shuntsthe resistor 18 by a relatively low impedance path, thereby reducing thevoltage drop thereacross. Thus, resistor 18 may be chosen to have alarge value to provide proper regulation with low power requirements,and yet the regulator tubes will be automatically ignited since resistor13 is shunted during the interval in which tubes 10 and 11 are beingignited. Resistor 19 is chosen to have a large value to reduce the powerloss thereacross to a small value during normal operation of theregulator.

Alternatively, a fuse may be utilized in lieu of condenser 25, the fusebeing chosen to have a rating such that it will rupture when the voltageregulator tubes are ignited, at which time the combined components ofthe load current and regulator current which flows therethrough exceedsthe rated amperage of the fuse. Use of a fuse, however, precludesrefiring of the regulator tubes in the event they are extinguishedbefore the supply source voltage B drops below the minimum value atwhich firing of the regulator tubes can be effected.

The regulator illustrated in Fig. 2 is similar to that of Fig. 1 andincludes a supply source B which is adapted to be connected, as byswitch S across the series cir cuit comprising regulating resistor 33and cold-cathode tubes 31 and 32 which are diode connected in serieswith each other. Tube 31 is lay-passed by a high impedance resistor 34,and resistor 33 is shunted by an R.-C. firing circuit comprising seriesconnected resistor 35 and condenser 36. The load 37 is coupled acrossthe regulator .by the drop across conditions, the regulator can be -fireunder connit' tubes by way of a filter circuit cornrising ballastresistor 38 and condenser 39. A resistor L is connected in shunt withresistors 33 and As is apparent, the resistor lfl reduces the voltagedrop across resistor 33, due to the flow of load current and thecharging current of condenser 39. In this manner, tubes 3i and 32 may becaused to ignite on an even lower differential between the supplyvoltage B and the composite conduction potential of tube 32 and thebreakdow potential of tube 31. Al though the regulated voltage appearingat terminal 42 does not follow the combined conduction potentials oftubes 31 and 32 as closely as in the embodiment illustrated in Fig. l,by proper choice of the values of resistors 33, 38 and 41 the degree ofregulation can be made high. Further, for a given supply potential, thevoltage at point d2 is varied only by the fraction of the change in thesustaining voltages of tubes 31 and 32. Since the conduction potentialof cold-cathode tubes is substantially constant only over anintermediate portion of the range of control gap currents, the resistor41 improves the linearity of the regulated output voltage at very lowand very high values control gap current.

The embodiment illustrated in 3 comprises a pair of cold-cathode tubes51 52 which are diode connected in series with each other and with aregulating resistor 53. Tube 51 and resistor are shunted by a highimpedance resistor 54 whercb voltage from the supply source B is appliedto tube o2; when the voltage regulator is connected thereto a" switch Sthereby causing tube 52 to ignite. Re ance 54 is made very high so as toreduce the power c am under normal operating conditions and condenser isconnected shunt with tube 52.. The condenser 55* is chosen to have asmall value so as to beco as charged r pidly upon connection of theregulator to the power sup; y. Condenser 55 thus serves to supply aportion of the initial surge of current through tube 52 upon ignitionthereof, and therefore reduces the voltage drop act s resistor whichwould tend to cause the tube to extinguished. A series do cuitcomprising resistor 56 and condenser 57' is connected acrosscord-cathode tubes and the load 63 is connected to the regulo .y of a11-0. circuit comprising ballast resistor denser A resistcr 63 isconnected resistors and di The resistor 63 supplies a porti to loadcurrent to load 63 and also a portion of the or 3 current of'condenserThus, by proper choi the values of resistors 53, 61 63, the drop .or 53can be made small so as to permit ignition of tubes 51 and 52 when thedifferential between the supply source potential and the composite cor"-otential of tube 52 and breakdown potential of tuo From the foregoingit is a cathode tube regulator circuits ments, provision is made a oneof the pair of series o ned thereby readying the non-cond theembodiments illustrated i made for shui ing the regulat pedance path A ra prec connecting the regulator to the s reducing the voltage dropduring the aforementioned interva ducting regulator tube can be ipotential which 875C mue for firing. In and 2, provision is ors by a lowimrval after c reg lating resistor s that the non-conply source 1ecomposite tion potential of he t ignited r gulator tube breakdown potenviding the shunt across r ating c n comes conductively inerttive l uctng tube.

r which beoperating omatically urce potential and high regulatingresistor impedance. In this manner a highly regulated output voltage isobtained with comparatively low regulator power consumption and from alow potential source.

It has been further ascertained that a continuously connected shuntacross the regulating resistor and the output filter resistor iseffective to reduce the potential drop across the regulating resistor toperm-it automatic ignition of both cold-cathode tubes at low supplysource potentials.

As is apparent from Figs. 2 and 3, before the coldcathode tubes becomeconducting, the relative magnitudes of the component of the load currentwhich flows through the regulating and ballast resistors and thecomponent which flows through the resistor in shunt therewith isdetermined by the relative impedances of the parallel paths. The dropacross the regulating resistor before the regulator tubes becomeconducting can thus be made small so that the tubes will automaticallyignite on low supply source potentials. However, after conductionthrough the tubes is established, the regulator tubes exercise acontrolling effect on the current l'low through the parallel paths, andthe output potential of the regulator is then, to a great extent,determined by the conduction potential of the cold-cathode tubes.Further, the provision of the shunting resistor reduces the variationsin the regulated output voltage due to variations in the conductionpotential of the cold-cathode tubes.

The voltage regulator tubes become extinguished at a relatively lowersupply source potential than is necessary to ignite the tubes. Theregulator then effectively drops out of the circuit and the outputvoltage is determined by the supply source potential and the drop acrossthe regulating resistor and output filter resistor. Since the regulatorcontinues operation when the differential between the supply sourcepotential and the conduction potential of the regulator tubes is small,the output voltage rise when the tubes become extinguished is not large,and for some tubes may be within the permissible range of outputvoltage.

Fig. 4 is a curve illustrating the variations in output voltage as thesupply potential decreases. The initial portion of the curve betweenpoints A and B indicates the regulated output voltage when the regulatoris in operation. The line B, C constituting the voltage rise when theregulator drops out, and the line C, D indicates the output voltagevariation after the voltage regulator drops out.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore understoodthat Within the scope of the appended claims the invention may bepracticed otherwise than as specifically described.

What is claimed as new and desired to be secured by letters Patent ofthe United States of America is:

1. A voltage regulator for maintaining a substantially constant voltagebetween the terminals of an electrical device supplied from a variablepotential direct current source comprising, in combination, a pair ofcold-cathode tubes each having a control gap; a first series circuitadapted to be connected across the source to be regulated and includingsaid cold-cathode tubes and a regulating resistor; and a second seriescircuit having a connection in common with said regulating resistor andadapted to interconnect said tubes 'ith said source at said commonconnection; said second series circuit including an impedance elementconnected to provide a conductive path shunting one of said tubes andhaving an impedance which is high as compared to the control gapconduction potential of said one of said cold-cathode tubes to therebyelfectuate ignition of theother of said tubes in response to connectionof said regulator to the source to be regulated, and low impedancecircuit means in shunt with said regulating resistor for by-passing saidregulating resistor with a low impedance path during the interval inwhich conduction is established in said cold-cathode tubes.

2. A voltage regulator for a variable potential direct current sourcecomprising a first series circuit including a pair of cold-cathode tubesand a regulating resistor adapted to be connected across the source tobe regulated, a second series circuit including a ballast resistor andsaid pair of cold-cathode tubes adapted to be connected to a loadcircuit, and means for igniting said coldcathode tubes in response toconnection of said first series circuit to the source to be regulated,said igniting means including an impedance element in shunt with one ofsaid tubes and means connected to said regulating resistor for reducingthe potential drop across said regulating resistor due to the flow ofload current through the regulator.

3. A voltage regulator for a variable potential direct current sourcecomprising a first series circuit including a pair of cold-cathode tubesand a regulating resistor adapted to be connected across the source tobe regulated, a second series circuit including a ballast resistor andsaid pair of cold-cathode tubes adapted to be connected to a loadcircuit, and means for igniting said cold-cathode tubes in response toconnection of said first series circuit to the source to be regulated,said igniting means including an impedance element in shunt with one ofsaid tubes and means including an impedance element in shunt with saidregulating resistor and said ballast resistor for reducing the potentialdrop across said regulating resistor due to the flow of load currentthrough the regulator.

4. A voltage regulator for a variable potential direct current sourcecomprising a first series circuit including a pair of cold-cathode tubesand a regulating resistor adapted to be connected across the source tobe regulated, a second series circuit including a ballast resistor andsaid pair of cold-cathode tubes adapted to be connected to a loadcircuit, and means for igniting said cold-cathode tubes in response toconnection of said first series circuit to the source to be regulated,said igniting means including an impedance element in shunt with one ofsaid tubes and means including a series R.-C. circuit in shunt with saidregulating resistor for reducing the potential drop thereacross for apredetermined time interval after connection of the regulator to thesource to be regulated.

5. A voltage regulator for a variable potential direct current sourcecomprising, in combination, a first series circuit including a pair ofcold-cathode tubes and a regulating resistor adapted to be connectedacross the source to be regulated; a second series circuit including aballast resistor and said pair of cold-cathode tubes adapted to beconnected to a load circuit; and means for igniting said cold-cathodetubes in response to connection of said first series circuit to thesource to be regulated; said igniting means including an impedanceelement in shunt with one of said tubes, means including an impedanceelement in shunt with said regulating resistor and said ballastresistor, and a series R.-C. circuit in shunt with said regulatingresistor for reducing the potential drop across said regulating resistorfor a predetermined time interval after connection of said regulator tothe potential source to be regulated.

6. A voltage regulator device including a pair of input terminalsenergized from a voltage source to be regulated and a pair of outputterminals for applying the derived regulated voltage to a utilizationcircuit, one terminal of each of said input and output terminals beingconnected to form a common terminal; a pair of coldcathode tubesconnected in series circuit relation to define a high potential terminaland a low potential terminal with said low potential terminal beingconnected to said common terminal; and an impedance circuitinterconnected between the other terminals of said input and outputterminals and having an intermediate terminal connected to said highpotential terminal for igniting said cold-cathode tubes in response tocurrent applied to said input terminals from the voltage source to beregulated whereby the voltage appearing at the output terminals isthereby regulated; said impedance circuit including a first impedanceelement connected to provide a conductive path shunting one of saidtubes and to apply an igniting potential to the other of said tubes, asecond impedance element for applying an igniting potential to said oneof said tubes a predetermined interval of time after ignition of saidother of said tubes, a third impedance element interconnected betweensaid intermediate terminal and said other terminal of said outputterminals and characterized by the property of directly varying itsimpedance in accordance with the variations in current flowingtherethrough, and voltage dropping means connected to said secondimpedance element for reducing the potential drop thereacross due to theflow of current through said tubes.

7. The device of claim 6, wherein said voltage dropping means comprisesa series R.-C. circuit connected in shunt with said second impedanceelement.

8. The device of claim 6, wherein said voltage dropping means comprisesa resistor connected in shunt with said second and third impedanceelements.

9. The device of claim 7, wherein said first impedance element isconnected in shunt with said second impedance element and said one ofsaid tubes; and further including a capacitive reactance connectedacross the anode-cathode circuit of said other of said tubes.

10. The device of claim 6, wherein said voltage dropping means comprisesa resistor connected in shunt with said second and third impedanceelements, and a series R.-C. circuit connected across said secondimpedance element.

References Cited in the file of this patent UNITED STATES PATENTS2,524,325 Mentzes Oct. 3, 1950 2,554,800 Steiner May 29, 1951

